[Reduced sensitivity of glycerinated rabbit m.psoas fibers to diprotonated vanadate during decrease in pH]

Vanadate (Na3VO4) action of the isometric force of maximal Ca2(+)-activated fibre has been studied at pH from 6.3 to 7.3. Acidification was shown to decrease the force declining vanadate effect: appearance of the dissociation constant estimated from force--H2VO4--dependence increases about two-fold following the pH decreasing from 7.3 to 6.3. Therefore the well-known decline of the force at acidification is accompanied by a decrease of the sensitivity to vanadate. These both phenomena can have a common nature and reflect, for example, a decreasing complex AM.ADP+ responsible for the force and interaction with vanadate. Our findings permit to think that the changes in pH with fatigue increasing the diprotonated form of phosphate simultaneously reduce the sensitivity of the contractile system to this form.